129858761424domain: NAppears in sequencesa(0)=0, a(1)=2 then a(n) = a(n-2) + 2*sqrt(8*a(n-1)^2 + 8*a(n-1) + 1).at n=15A053141a(n) = (2*Pell(n+1) - (1+(-1)^n))/4.at n=30A105635Expansion of (1-3*x) / (1-5*x-5*x^2+x^3).at n=15A108475